Earth’s centre is out of sync

We all know that the Earth rotates beneath our feet, but new research from ANU has revealed that the centre of the Earth is out of sync with the rest of the planet, frequently speeding up and slowing down. Associate Professor Hrvoje Tkalcic from the ANU College of Physical and Mathematical Sciences and his team used earthquake doublets to measure the rotation speed of Earth's inner core over the last 50 years. They discovered that not only did the inner core rotate at a different rate to the mantle - the layer between the core and the crust that makes up most of the planet's interior - but its rotation speed was variable. "This is the first experimental evidence that the inner core has rotated at a variety of different speeds," Associate Professor Tkalcic said. "We found that, compared with the mantle, the inner core was rotating more quickly in the 1970s and 1990s, but slowed down in the 80s. The most dramatic acceleration has possibly occurred in the last few years, although further tests are needed to confirm that observation. "Interestingly, Edmund Halley, namesake of Halley's Comet, speculated that the inner shells of the Earth rotate with a different speed back in 1692." Scientists have so far assumed the rotation rate of the inner core to be constant because they lacked adequate mathematical methods for interpreting the data, says Associate Professor Tkalcic.